There is controversy as to whether weight loss in HIV-positive persons is due to malnutrition or to alterations in metabolism. The principal goal of this project is to measure the relative importance of these two possible mechanisms of weight loss in HIV-positive persons. In a cross-sectional analysis, dietary intake and metabolic rate will be measured in 30 HIV-positive men who have lost at least 5% of their body weight over the previous 6 months. These measurements will be compared to those of 30 HIV-positive men who have not lost weight.